1. Field of the Invention
The present invention relates generally to the field of antifriction bearings and housings for such bearings. More particularly, the invention relates to a molded polymeric bearing housing including features advantageous in certain applications, such as in the food and beverage industries.
2. Description of the Related Art
A wide range of applications exist for antifriction bearings, such as ball bearings, roller bearings, needle bearings and the like. In many industrial and material handling systems, such bearings perform a fundamental function of permitting rotating machine elements to turn with little resistance and thereby to effectively transmit power and motion between drive system components. Applications for such bearings include conveyors, mixers, pump drives, and the like, to mention just a few.
In general, bearings of the type commonly used in most industries include an inner race, an outer race, and a plurality of antifriction bearing elements disposed therebetween. The bearing elements are captured by the races and permit the races to rotate freely with respect to one another. The bearing assembly is typically installed in and supported by a housing. A number of housing types are known and are in common usage, including pillow block styles, two and four bolt flanged styles, take-up frame styles, and so forth. In addition to supporting the bearing inserts, such housings include features that permit them to be easily attached to machine frames and other support structures at the application. Depending upon the housing style, these features typically include support feet or flanges traversed by apertures for receiving fasteners. Once mounted on the machine frame, a base surface of the bearing housing generally abuts the machine frame and forms a solid foundation for both the bearing insert and for the machine elements held in rotation by the bearing insert.
Housings of the type described above are commonly made of a variety of materials depending upon the particular application, the loads to which the bearing insert will be subjected and the environmental conditions of the application. For example, in most bearing styles, metal housings provide sufficient mechanical support and resistance to loads. However, such metal housings are not well-suited to certain applications. Specifically, in certain industries health or environmental constraints may make the use of metal bearing housings difficult or impossible. In the food and beverage industries, for example, health requirements often necessitate frequent washing of processing and material handling equipment including bearings and their housings. Under such conditions, conventional metal housings may tend to corrode or otherwise degrade in ways that would contaminate the working conditions of the machinery and/or the product processed by the machinery. Similarly, in chemical processing industries and certain marine applications the presence of corrosive substances may significantly reduce the life of conventional metal bearing housings. In response, the industry has began to employ alternative materials for bearing housings, including certain plastics.
In general, conventional plastic bearing housings are available in the same styles as their metal counterparts. Thus, pillow block bearing styles are available from various manufacturers which differ only slightly from designs available in metal. However, due to manufacturing and processing constraints unique to plastic materials certain features of conventional plastic bearing housings present drawbacks which make them unsatisfactory in specific industrial applications. For example, due to the particular geometry of some bearing housing styles, such as pillow block housings, large volumes of the housing may be present in regions of the housing, while relatively thin or small volumes are present in other regions. Due to the exigencies of conventional injection molding processes, most conventional designs therefore include ribbed structures in the larger volumes regions to provide the requisite structural integrity, while providing sufficient material flow and curing in those regions and avoiding drawing during the curing process. In pillow block designs, for example, ribs are commonly provided below the bearing support and the lower support flanges. Some or all of these ribs contact the machine frame when the housing is installed, leaving voids or cavities below the bearing housing between the housing and the machine frame. While the plastic housing itself may perform adequately under frequent and repeated washdowns, such interstices left between the housing and the machine frame tend to remain wet or moist. Over time, these areas tend to promote the growth of fungi, molds, bacteria and other microorganisms reducing the utility of the housing and requiring additional downtime for cleaning or even replacement of the housing.
Industry responses to these problems have been less than satisfactory. For example, one response has been to fill the voids or interstices at the base of the bearing housing prior to placing the housing in service. In one known approach, the entire base of the housing is overmolded with an elastomeric or thermoplastic elastomer filler in an attempt to cover the voids and cavities. However, this solution provides a product which is non-uniform in appearance, and which requires additional tooling and manufacturing processes, adding to the cost of the final product.
There is a need, therefore, for an improved polymeric bearing housing which does not suffer from the drawbacks described above. In particular, there is a need for a bearing housing which can be used in applications where environmental or health conditions require superior resistance to corrosion, while inhibiting the proliferation of microorganisms.